1. Field of the Invention
The present invention relates to spacers incorporated in picture display devices such as a plasma display, a field emission display and the like, and to a method of producing the same.
2. Description of the Prior Art
There have, in recent years, been developed picture display devices such as a plasma display panel (PDP), a plasma address liquid crystal (PALC) panel and a field emission display (FED). These picture display devices are equipped with a face plate for displaying picture and a back plate arranged maintaining a gap with respect to the back surface of the face plate and in parallel therewith and, further, with plural spacers maintaining a suitable gap to maintain space for electric discharge between the face plate and the back plate. That is, in these picture display devices, the interiors of the devices must be maintained vacuum to form space for electric charge and, hence, the face plate and the back plate must be prevented from being deflected by the atmospheric pressure. It therefore becomes necessary to provide plural spaces of a suitable height (length) between the face plate and the back plate.
In the above-mentioned field emission display, for example, the back plate is provided with plural electron emissive elements that generate electron rays which are then accelerated to have the phosphor formed on the face plate emit light to display the picture. In this field emission display, further, the gap of not smaller than 500 xcexcm must be maintained between the face plate and the back plate in order to prevent abnormal electric discharge between the electron emissive elements and the phosphor as well as to obtain a desired brightness by controlling the current density of the electron rays and the acceleration condition. Accordingly, the spacers must have a height of not smaller than 500 xcexcm.
As a method of producing the above-mentioned spacers, there has been known a method of forming spacers integrally with the back plate or the face plate. In the plasma display panel, for example, a paste is prepared by adding an organic resin (acrylic binder or dispersant) and an organic solvent to a mixture of a glass and a ceramic filler (softening point-improving agent or pigment) such as ZrO2, SiO2, etc., a molded article of spacers is formed on the surface of the glass plate which may be an alkali borosilicate glass by using the paste, and the molded article is fired at a temperature (e.g., about 550xc2x0 C.) at which the glass plate does not shrink thereby to form spacers on the surface of the glass plate. The molded article of spacers is obtained by printing the paste onto the surface of the glass plate or by using a mold. This method makes it possible to form spaces having a thickness of usually, about 40 xcexcm and a height of about 150 xcexcm together with the glass plate. The glass plate is used as a face plate or as a back plate.
According to the method of forming spacers integrally with the glass plate which serves as the face plate or the back plate by firing the molded article of spacers formed on the glass plate by using the paste containing glass and ceramic filler as described above, however, it is not allowed to precisely form the spacers due to shrinkage by firing and, besides, the spacers are deformed or peeled off the glass plate.
That is, in firing the molded article of spacers, the glass plate supporting the molded article does not almost shrink but the molded article (spacers) only shrinks, developing a difference of shrinkage between the spacers and the glass plate and arousing the above-mentioned problems.
When the spacers of a small height are formed, the shrinkage in the spacers caused by firing decreases due to the locking force of the glass plate, and the above-mentioned problem does not almost occur. Therefore, the above-mentioned method of forming the spacers is adapted to the plasma display panel which needs have spacers of a small height. As the height of the spacers increases, however, the shrinking force of the spacers becomes greater than the locking force of the glass plate; i.e., it becomes no longer possible to decrease the shrinkage of the spacers caused by firing, and the above-mentioned problem becomes conspicuous. Accordingly, the above-mentioned method of forming the spacers could not be applied to the field emission display that requires spacers having a height of not smaller than 500 xcexcm. Even if it could be applied, the thickness of the spacers must be very increased. After all, the method of forming such spacers is not suited for the field emission display.
In the field emission display, therefore, a glass or ceramics after firing is cut into the shape of spacers and is stuck to the surface of the glass plate that serves as the face plate or the back plate to form spacers. This method, however, forms the spacers having a low dimensional precision or a low positional precision requiring laborious work and, besides, is not suited for decreasing the thickness of the spacers or the gap among the spacers.
In the field emission display, further, electrons emitted from the electron emissive elements impinge upon the wall surfaces of the spacers present close to the trajectory of electrons causing the wall surfaces of the spacers to be electrically charged. That is, the electron rays generated from the electron emissive elements are bent by the electric charge on the wall surfaces of the spacers, whereby the electron rays fail to arrive at predetermined positions on the face plate maintaining precision, causing the picture displayed on the front plate to be distorted, developing abnormal electric discharge between the electron emissive elements and the spacers, and decreasing the density of electron rays arriving at the phosphor, making it difficult to obtain a desired brightness.
It is therefore an object of the present invention to provide spacers which are effectively prevented from being deformed or peeled due to the shrinkage caused by firing and are further effectively prevented from being electrically charged, and a method of producing the same.
Another object of the present invention is to provide spacers that are formed integrally with the face plate or the back plate, and are particularly effectively used for the field emission display, and a method of producing the same.
A further object of the present invention is to provide a method of producing spacers, effectively preventing the shrinkage caused by firing even in forming spacers having a height (length) of not smaller than 500 xcexcm, and effectively preventing deformation or peeling caused by shrinkage due to firing.
A still further object of the present invention is to provide a method of producing spacers, which makes it possible to decrease the thickness and the gap.
According to the present invention, there are provided spacers disposed between a face plate which displays a picture and a back plate that faces a back surface of the face plate to maintain space for electric discharge therebetween, wherein said spacers are formed of a sintered product having a structure in which at least one kind of metal selected from the group consisting of Si, Zn, Al, Sn, Cu and Mg is dispersed in a glass.
According to the present invention, further, there is provided a method of producing a ceramic by preparing a molded article by using a mixture of a glass and at least one kind of metal selected from the group consisting of Si, Zn, Al, Sn, Cu and Mg, and firing the molded article in an oxygen-containing atmosphere to oxidize part of said metal.
According to the present invention, there is further provided a picture display device comprising a face plate for displaying a picture having a phosphor layer formed on a back surface thereof, a back plate facing the back surface of the face plate and having electron emissive elements on the surface thereof on the side of the face plate, and spacers provided between the face plate and the back plate to maintain space for electric discharge therebetween, wherein said spacers are formed of a sintered product having a structure in which at least one kind of metal selected from the group consisting of Si, Zn, Al, Sn, Cu and Mg is dispersed in a glass.
The spacers of the present invention have a distinguished feature in that they are formed of a sintered product having a structure in which a predetermined metal (Si, Zn, Al, Sn, Cu or Mg) is dispersed in the glass.
That is, electrically conducting property is imparted to the spacers due to the metal dispersed in the glass. Therefore, the spacers arranged near the electron emissive elements are effectively prevented from being electrically charged, effectively avoiding such problems as distortion of the picture or drop in the brightness specific to the field emission display caused by the electric charge in the spacer.
A ceramic which constitute such spacers is obtained by firing a molded article (having a shape of the spacer) of a mixture of the glass and the metal, in an oxygen-containing atmosphere. Due to the firing, the metal is partly oxidized to undergo the volume expansion. Shrinkage of the molded article due to firing is relaxed by the volume expansion of part of the metal. Therefore, the spacers of the invention having the metal dispersed in the glass can be formed integrally with the insulating plate such as face plate or back plate of the picture display device. Therefore, the spacers shrink little through firing even when they have a height of not smaller than 500 xcexcm, and are prevented from being deformed or from being peeled off the glass plate. Besides, the thickness of the spacers needs not be unnecessarily increased offering advantage from the standpoint of decreasing the thickness of the spacers and decreasing the gap among plural spacers.
Thus, the spacers of the present invention are particularly effectively utilized for the field emission display (FED) that requires spacers having a height of not smaller than 500 xcexcm.